Electrically powered artificial lighting has become ubiquitous in modern society. Electrical lighting devices are commonly deployed, for example, in homes, buildings of commercial and other enterprise establishments, as well as in various outdoor settings.
In conventional lighting devices, the luminance output can be turned ON/OFF and often can be adjusted up or dimmed down. In some devices, e.g. using multiple colors of light emitting diode (LED) type sources, the user may be able to adjust a combined color output of the resulting illumination. The changes in intensity or color characteristics of the illumination may be responsive to manual user inputs or responsive to various sensed conditions in or about the illuminated space. The optical distribution of the light output, however, typically is fixed. Various different types of optical elements are used in such lighting devices to provide different light output distributions, but each type of device has a specific type of optic designed to create a particular light distribution for the intended application of the lighting device. The dimming and/or color control features do not affect the distribution pattern of the light emitted from the luminaire.
To the extent that multiple distribution patterns are needed for different lighting applications, multiple luminaires must be provided. To meet the demand for different appearances and/or different performance (including different distributions), a single manufacturer of lighting devices may build and sell thousands of different luminaires.
Some special purpose light fixtures, for example, fixtures designed for stage or studio type lighting, have implemented mechanical adjustments. Mechanically adjustable lenses and irises enable selectable adjustment of the output light beam shape, and mechanically adjustable gimbal fixture mounts or the like enable selectable adjustment of the angle of the fixture and thus the direction of the light output. The adjustments provided by these mechanical approaches are implemented at the overall fixture output, provide relatively coarse overall control, and are really optimized for special purpose applications, not general lighting.
There have been more recent proposals to develop lighting devices offering electronically adjustable light beam distributions, using a number of separately selectable/controllable solid state lamps or light engines within one light fixture. In at least some cases, each internal light engine or lamp may have an associated adjustable electro-optic component to adjust the respective light beam output, thereby providing distribution control for the overall illumination output of the fixture.
Although the more recent proposals provide a greater degree of distribution adjustment and may be more suitable for general lighting applications, the outward appearance of each lighting device remains the same even as the device output light distribution is adjusted. There may also be room for still further improvement in the degree of adjustment supported by the lighting device.
There also have been proposals to use displays or display-like devices mounted in or on the ceiling to provide variable lighting. The Fraunhofer Institute, for example, has demonstrated a lighting system using luminous tiles, each having a matrix of red (R) LEDs, green (G), blue (B) LEDs and white (W) LEDs as well as a diffuser film to process light from the various LEDs. The LEDs of the system were driven to simulate or mimic the effects of clouds moving across the sky. Although use of displays allows for variations in appearance that some may find pleasing, the displays or display-like devices are optimized for image output and do not provide particularly good illumination for general lighting applications. A display typically has a Lambertian output distribution over substantially the entire surface area of the display screen, which does not provide the white light intensity and coverage area at a floor or ceiling height offered by a similarly sized ceiling-mounted light fixture. Liquid crystal displays (LCD) also are rather inefficient. For example, backlights in LCD televisions have to produce almost ten times the amount of light that is actually delivered at the viewing surface. Therefore, any LCD displays that are to be used as lighting products need to be more efficient than typical LCD displays for the lighting device implementation to be commercially viable.
Other proposals have been directed to utilizing transparent image displays that allow an image to be displayed while remaining at least partially transparent. In particular, such transparent image display is collocated with a general illumination device and illumination generated by the general illumination device “passes through” the transparent image display. However, existing transparent image displays tend to offer unacceptable trade-offs between various criteria such as transparency, brightness, contrast ratio, and resolution. For example, a transparent image display may offer high transparency, but only moderate resolution. In another example, a transparent image display may offer high resolution, but low transparency or a limited color gamut. As such, existing transparent image displays are not optimal for combination with a general illumination device.